Method of making grinding wheel mounts

ABSTRACT

An abrasive wheel comprising a disc having a central aperture therein and a one-piece plastic hub molded onto the disc, the hub including a threaded aperture, a broad circular flange, and a tubular projection extending through the aperture in the disc and into close cooperation with a countersunk portion at the opposite side of the disc from the main body of the hub and the circular flange.

United StatesPatent 1191 Sherman Apr. 2, 1974 54] METHOD OF MAKING GRINDING WHEEL 2,958,166 11/1900 Foland 51/358 MOUNTS 1 3,081,584 3/1953 Bullard 51/200 3,395,417 8/1968 Matouka 51/358 x Filed:

William F. Sherman, 2 Burtenmar Cir., Paxton, Mass. 01612 Jan. 22, 1971 Appl. No.: 108,789

Inventor:

US. Cl 51/376, 51/298, 117/652, 264/267 Int. Cl... B24b 17/00, C08h 17/12, C08g 51/12 Field of Search 51/209, 558, 376, 378, 51/168 References Cited UNITED STATES PATENTS Patt 51/358 Wiley 51/358 Primary Examiner-Othell M. Simpson Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT An abrasive wheel comprising a disc having a central aperture therein and a one-piece plastic hub molded onto the disc, the hub including a threaded aperture, a broad circular flange, and a tubular projection extending through the aperture in the disc and into close cooperation with a countersunk portion at the opposite side of the disc from the main body of the hub and the circular flange.

4 Claims, 4 Drawing Figures PATENTEDAPR 2:914 5 3.800.483

SHEEIIUFZ A vul H6. 3 I IINVEN'TOR WILLIAM SHERMAN PATENTEUAPR 219m 3.800.483

sum 2 or 2 INVENTOR WILLIAM SHERMAN BY 3 2; W

ATTORNEYS METHOD OF MAKING GRINDING WHEEL MOUNTS BACKGROUND OF THE INVENTION tional or impact removing of rough spots on various items such as weldments; concrete surfaces, machine work, and the like is well known. The US. Pat. No. 3,081,584 granted Mar. 19, 1963 to Robert A. Bullard, discloses a conventional abrasive wheel presently in commercial use. This abrasive wheel consists basically of a central base member to provide connection to a portable hand grinder or other machine for supplying the motive force and a disc member attached to the central base member. The disc member has usually assumed the form of a screen impregnated with an abrasive and a bonding agent. I

The abrasive wheel of the Bullard patent utilizes a central mounting member with a considerable flange for providing sufficient surface to permit a fastening of the abrasive disc onto the central member by means of an epoxy resin cement. To further insure a sufficient bonding between the central mounting member and the abrasive disc, the tubular portion of the central mounting member that extends through the abrasive disc is generally ball swaged, to provide a counter sunk portion of the tubular projection against the lower surface of the abrasive disc. Thus, the manufacturing process of the presently accepted abrasive wheel requires a two-step process for joining an abrasive disc to a metallic central mounting member. This process includes the step of adhering by an epoxy resin the flange of the central mounting member to the disc and further the step of mechanically deforming the metallic central member by countersinking or .ball swaging the central mounting member onto the lower surface of the abrasive disc. Generally the epoxy material must be cured before the abrasive wheel is capable of use.

Another form of an abrasive wheel used for snaggingprovides a replaceabledisc having a central hole which is mounted by a coaction of washers or clamps on either side of the disc onto a grinder machine. Vibrational problems in loosening the washers and clamps have been a problemv in utilizing this form of abrasive wheel. Likewise a considerable amount of time and effort must be utilized by the operatorin mounting the abrasive wheel on the grinder or chang ing an abrasive disc.

SUMMARY OF THE INVENTION The present invention is designed to provide a method or process of manufacturing abrasive wheels in a highly economical and efficient manner. This is accomplished by molding a strong thermoplastic mounting hub directly onto the abrasive wheel. By appropriately designing the abrasive wheel the thermoplastic hub can be molded to form both a chemical and mechanical bond in a single step that removes any necessity of an elaborate finishing process which would in clude a prolonged curing process ofan epoxy adhesive material. 1

BRIEF DESCRIPTION OF THE DRAWINGS The best mode contemplated of carrying forth the process of the present invention will be described in detail below in connection with the accompanying drawings in which:

FIG. 1 is a perspective view of an abrasive wheel produced according to the process of the present invention;

FIG. 2 is a perspective crosssectional view of the abrasive wheel of FIG. 1;

FIG 3 is a sectional view of the molding equipment utilized in the inventive process; and 7 FIG. 4 is a cross-sectional view of the molding apparatus of FIG. 3 during operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT The process of the present invention is generally accomplished by inserting a specifically designed abrasive wheel which may be preheated into the stationary mold half of one side of a conventional plastic mold and inserting a polished chrome plated hardened steel insert through the abrasive wheel disc by closing the die to form the mold cavity. A molding machine forces a thermoplastic into the mold and more specifically, in the preferred process the thermoplastic material is of that family known as polycarbonates sold under the trademark MERLON, which is a thermoplasticresin that is manufactured by the process of either, phosgenation of dihydric phenols, usually bisphenol-A; or ester exchange between diaryl carbonates and dihydric phenols, usually between diphenyl carbonate and bisphenol-A; or interfacial polycondensation, generally accomplished with a chlorinated aliphatic solvent,

. aqueous sodium hydroxide, bisphenol-A and phosgene.

The polycarbonate polymer produced by any one of the above methods generally requires for the present process to have a softened or liquid state in the temperature range of approximately 400 to 600 F. The general base structure of the polycarbonate polymeris as follows:

Compression ratio r l.74-5.5 Specific gravity (density) 1.2 Specific volume. cu. in./lb. 23.0 Softening Range F 4004200 Tensile strength. p.s.i. 8.0009.500 Elongation, 100.04 30.0 Flexural yield strength. p.s.i. 13,500 Impact strength, ft. Ib./in. of notch x in.

notched bar). Izod test (AXIS in. bar) Compression strength, p.s.i. 12,500

Some possible injection molding parameters, for the aromatic polycarbonate are as follows:

1. Cylinder, or stock temperatures of the material, 400 to 600 F. Most parts can be molded in the range of 500 to 580 F but as part configuration, and shot size compared to the capacity of the machine will vary, it is sometimes necessary to use the lower or the higher temperatures.

2. Mold Temperature 150 to 250". F., some molds do not have to be heated or cooled, but the average ideal mold temperature for most polycarbonate parts is, 180 F.

3. Injection Pressure 5,000 p.s.i. to 30,000 p.s.i. The average is usually from three quarters, to the full amount that the machine can supply, 20,000 p.s.i. at the orifice of the nozzle gives the best polycarbonate parts, as a rule.

4. Cycle. This will depend on the part to be molded, however; parts are governed by their thickness, and it is necessary to inject the material rapidly for most parts, but for very thick parts, slower injection is required, thus, slowing the overall cycle. Parts of good quality, one-fourth inch thick, have been molded in twenty seconds. Because of its high heat distortion point, polycarbonate can be molded, using shorter cycles than most other plastics, as it cures in the mold, or sets up, quite rapidly.

Other thermoplastic resins that are capable of being used in place of polycarbonate are polypropylenes,

both homopolymer and copolymer'and the A.B.S. family of plastic (a combination of acrylonitrile, butadiene and styrene). The high impact strength and high heat distortion characteristics make them suitable for the present invention.

During the process of one form of the invention a compatibility between the particular thermoset plastic utilized in the abrasive disc of this invention has been found with the aromatic polycarbonate thermoplastic resin of the central hub member. In fact, it is believed that the thermoset plastic forms a chemical bond with the thermoplastic plastic to increase the strength of the connection between the hub and the abrasive disc. Generally, the abrasive disc comprises a base of a fiberglass web or mesh containing abrasive powder of a well known type such as aluminum oxide and a phenolic resin to serve as a bonding agent.

Turning now to'the thermoset plastic material applicable to the present invention, it has been found that phenol formaldehyde resins prepared by the one-stage or two-stage method are extremely suitable for use in the present invention.

In phenol formaldehyde resins prepared by the onestage" method, the formaldehyde in a concentration greater than one mol per mol of phenol is used with an alkaline catalyst, such as caustic soda in order to produce an ammonia-free resin.

In the two-stage method, an excessive amount of phenol together with formaldehyde and an acid catalyst. such as hydrochloric or sulfuric acid, are reacted to form what is known as a novalak. In this method, additional formaldehyde is required in order to complete the final polymerization, and this is usually attained in the form of hexamethylenetetramine (commonly known as hexa).

Between the two types of phenol-formaldehyde resins, those produced by the two-stage method are preferred for use in this invention, since they are known to have a far longer shelf life than those prepared by the one-stage method.

Illustrative of these phenol-formaldehyde resins and specifically the movalak resins, are the so-called Durez Resins produced by the Hooker Chemical Company.

These resins have a mean molecular weight of about 500 and an average molecular weight ranging from 450 to 550.

While not wishing to be limited to any particular theory, it is believed that the resulting strength characteristics of the grinding wheel of the present invention are attained through the cross-bonding between the thermosetting resin and thermoplastic polycarbonate during the molding process. In addition, the possibility of a Vander Wal bonding resulting from the interaction of the molecular poles of the polymers appears to be a distinct possibility.

At this juncture, it should be mentioned that the phenolic resins contemplated for use herein are not limited in number. That is, any phenol-formaldehyde resin prepared in the aforementioned manner and from the aforementioned components will suffice, providing, however, it does not detract from the goals of the present invention.

However, the salient feature here resides in the fact that the thermoplastic component (polycarbonate) and the thermosetting component (phenol-formaldehyde resin) when united, form an extremely strong bond. This is totally unexpected in view of the known properties between these two types of materials. Hence, the thermosetting component (herein defined as one which is already cured and being in the molded state) would not be expected to create the strong chemical and mechanical bond as achieved herein.

As an additional feature of the invention it would be possible to provide color coding in the plastics so that the color of the hub of a particular abrasive wheel would signify a particular size or type of disc thus removing any necessity to provide other indicia that would, for example, state a specific safety limit for the use of the abrasive wheel.

Referring to FIG. 1, the end product of the manufacturing process can be seen; The grinding wheel assembly 10 comprises basically an abrasive disc 12 and a hub 14. I

The abrasive disc generally comprises a number of layers of fiberglass mesh impregnated with a mixture of an abrasive, such as aluminum oxide or silicon carbide or some other appropriate abrasive with a bonding agent which in the preferred embodiment is a resinoid organic bond. Other bonds could include vitrified rubber, shellac or silicate. The hub member 14 in the preferred embodiment is an aromatic polycarbonate molded into the shape of a hexagonical nut 18. The base of the hub 14 includes a flange 16 which is connected with the hexagonical nut portion 18 by a generous radius 20 to remove any stress associated with a notched effect.

As can be seen in FIG. 2, the hexagonical nut 18 has a threaded aperture 22 and generally the top portion of the hexagonical nut 18 is appropriately countersunk. The lower surface of the abrasive disc 12 has a circular portion 24 removed to form a cavity. This permits the heat softened aromatic polycarbonate resin to form a round ring of plastic 26 to provide a mechanical bond between the hub 14 and the abrasive disc 12. Just as in the-top portion of the hub 14 the lower portion is generally countersunk and after the finishing operation, the hub 14 does not protrude below the lower surface of the abrasive disc 12. Utilizing an aromatic polycarbonate having a tensile strength in the range of from 8,000 to 9,500 psi, the preferredgrind wheel assembly will have a hub that is bonded to the abrasive disc 12 and which will have a strength stronger than the abrasive disc 12 itself. This form of polycarbonate material generally has an impact strength with values nearing that of most metals per unit weight.

Referring to FIGS. 3 and 4, the die assembly 28 comprising a movable mold half 30 and a stationary mold half 32 can be seen. On the back of the stationary mold half 32 is a locating ring 34 used to align the mold into the molding machine. The nozzle 36 of the molding machine passes between the locating ring and seats against the sprue bushing 38. A back plate 40 supports the locating ring 34 and provides a slot 42 with the sta-' tionary mold half 32. The slot 42. accommodates the dogs or clamps that are used to fasten the mold to the machine platen. Locating pins 44 extend from the surface of the stationary mold half 32. An alignment plate 46 is appropriately located vwith alignment dowels 48 to position the abrasive disc .12 in the die assembly. The movable mold half 30 has recesses which form-female mates 50 for the locating pins 44 of the stationary mold half 32. A central cavity 52 permitsthe movable half of the mold 30 upon-opening, to move back, allowing the ejector pin 51 to make contact with the end of the insert 54, thus pushing the entire molding free from the movable half of the mold. The insert 54 is preferably made of hard machine steel, chrome plated for both wear resistance and for easy removal from the molded part, has ahexagonical base 56, for positioning in the movable mold half 30. The central portion 58, of the insert 54, is round, and terminates in a threaded portion 60. A depression or cavity surrounds the insert 54 on the face of the movable mold half 30. This undercut depression 64 serves two purposes. It prevents the hot plastic from flashing'over the bottom surface of the abrasive disc 12 and it fu'rtherserves as a sprue puller, that is, it has enough undercut to hold the molded assembly to the face of the movable mold half until the ejector pin 51 contacts the insert 54 to loosen themold from the die. lt'is possible that the area may require a slight machine dressing with an end mill in a drill press after molding. The threaded portion of the insert 54 is preferably designed with a'rounded crown so that the roots. of the thread left in the hub 14 have a sufficient radius to preventany notch effect or stress risers.

The process of manufacturing the grinding wheel assembly 10. comprises placing the abrasivedisc 12 in a stationary mold half 32 of the die assembly 28. Preferably the abrasive disc is preheated to a temperature approximately between 150 to 200 F before the plastic injection step. The movable mold'half 30 with the aid of the locating pins 44 and female mates 50 is moved into position so that the insert 54 is inplace within the hub cavity of the stationary mold half 32. tremely important that the insert 54 be located perpendicular to the plane of the abrasive disc 12 since the abrasive wheel will be utilized-at a high rpm. In one preferred embodiment the die assembly 28 can be heated to a temperature between 1509 to 200 F and the abra- It is ex--.

sive disc 12 can likewise either be preheated or brought up to this temperature in the mold. The cylinder of the molding machine will be heated inthe range of 450 to 600 F. This temperature range will liquify the polycarbonate. An injection pressure which will be approximately 20,000 psi at the orifice of the nozzle can be utilized. The plunger or ram of the injection molding machine injects theliquid polycarbonate through the nozzle 36 and the sprue bushing 38 into the cavity that forms the hub 14. The softened aromatic polycarbonate flows around the threaded insert 54 that creates the threaded aperture 22 and finally through the aperture of the abrasive disc 12 into the circular portion 24 on the bottom side of the abrasive disc 12. The pressure of the polycarbonate around the abrasive disc 12 is approximately 1,000 to 1,200 psi. In a manner of a few seconds the aromatic polycarbonate material has hardened enough to permit the timer controlled plunger of the molding machine to return to its back position and receive another measured amount of aromatic polycarbonate plastic into the heating cylinder. After a few more seconds the mold will open and the entire grinding wheel assembly-will be stuck to the movable mold half 30 until the ejector pin 50 contacts the insert 54 to remove the grinding wheel 10 from the die assembly 28. The die assembly 28 is then reloaded with another abrasive wheel 12 and another insert 54 with the cycle being repeated. The insert 54 is removed from the grinding wheel assembly 10 andany sprue is cut off. Generally an end mill in a drill press will be required to dress the finished part and then it would be ready for hot stamping or painting if desired. The entire operation is performed in approximately 30 seconds. It is obvious that a die assembly can consist of a number of cavities and appropriate insert pins 54 so that several grinding wheel assemblieslO can be manufactured at the same time. The aromatic polycarbonate material will generally permit the insert 54 to be hand screwed out of the hub 14 while the aromatic polycarbonate ,is still in a heated condition. It is possible to modify the movable mold half 30 to permit an automatic revolving of the insert 54'before or after it has been contacted by the ejector pin 51 for the purpose of removing the insert 54 from the grinding wheel.

It is believed that the use of an aromatic polycarbonate plastic permits not only a mechanical bonding to the abrasive disc 12 but also permits achemical bonding with the thermoset phenolic resin which is utilized as the bonding agent in the abrasive disc 12. The combination of both the mechanical bond and the chemical bondin-a single operation provides a highly efficient and durable grinding wheel assembly not previously available to industry.

I claim:

1. An abrasive wheel comprising a disc impregnated with abrasive material and having a central aperture, a

'molded plastic unitary one piece hub secured to' thecentral portion of the disc, the main portion of the hub being generally at one side of the discfA tubular projection centrally located on the hub and extending through the disc aperture, the disc having a countersunk portion about the aperture at the opposite side of the disc from the main portion of the hub, the tubular projection having an annular portion extending outwardly into the area of the countersunk portion to overlap the disc in the area surrounding the aperture in the disc, and the hub including a broad integral flange hub comprises a material in the nature of a modified phenoline oxide.

4. The abrasive wheel of claim 1 including a bond between the disc and said hub, said bond including liquid phenol formaldehyde.

, Page 1 of 2 UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT N0. 3, 83

DATED 1 April 2, 1974 INVENTOR(S) William F. Sherman It is certified that error appears in the above-identified patent and'that said Letters Patent are hereby corrected as shown below:

Column 2, line 21, insert a comma after "wheel"; insert a comma after preheated";

line 22, insert a comma after "mold";

Column 3, line 44, delete "plastic" and insert --resin--;

line 52, after "phenol", insert a dash;

line 55, after "phenol", insert a dash;

line 63, change "novalak" to --novolak--;

Column 4, line 7, change "movalak" to --novolak--;

line 16-17, delete therrnosetting resin" and insert --thermoset plastic-;

line 30, delete "thermosetting" and insert -thermoset--;

line 34, delete "thermosetting" and insert --thermoset--;

line 54, delete "bond" and insert --bonding agent--; delete "bonds and insert -bonding agents--; insert a comma after "vitrified";

Page 2 of 2 UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,800,483 DATED Apr11 Z, 1974 mv moms) William F. Sherman Q It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 8, change "grind" to --grinding--;

line 43, delete "plastic" and insert -thermoplastic-q line 58, delete "plastic" and insert --thermop1astie--.

Signed and Scaled this Seventh Day of June 1977 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (0mm issiuner of Patents and, Trademarks 

1. An abrasive wheel comprising a disc impregnated with abrasive material and having a central aperture, a molded plastic unitary one piece hub secured to the central portion of the disc, the main portion of the hub being generally at one side of the disc. A tubular projection centrally located on the hub and extending through the disc aperture, the disc having a countersunk portion about the aperture at the opposite side of the disc from the main portion of the hub, the tubular projection having an annular portion extending outwardly into the area of the countersunk portion to overlap the disc in the area surrounding the aperture in the disc, and the hub including a broad integral flange extending laterally over the side of the disc having the main portion of the hub thereon, the hub thereby being physically locked to the disc.
 2. The abrasive wheel of claim 1 including a bond between the disc and the said hub.
 3. The abrasive wheel of claim 1 wherein the plastic hub comprises a material in the nature of a modified phenoline oxide.
 4. The abrasive wheel of claim 1 including a bond between the disc and said hub, said bond including liquid phenol formaldehyde. 